The sea serpent is long skinny (65-75 ft) deep-sea predator; essentially a giant snake with a ribbonlike body. It breathes air and can dive to about 300 feet (about 91 meters), holding its breath for 20-30 minutes. Although descended from venomous ancestors, sea serpents are becoming more of a constrictor type. Their neurotoxic venom is losing potency while their physical size and strength increase. They attack by wrapping around prey which can include large fish, marine mammals, and other sea monsters. They are rarely bothered, although occasionally a hungry deathfin or something else will try. Like other snakes, they can unhinge their jaws to swallow whole even very large prey (including a whole human or seal); and they may go nearly dormant for a while after a big meal. The sea serpent is edible similar to other snakes: most people won't touch it, but some like it a lot.

Sea serpents are widespread across suitable habitat. They are ovoviviparous, carrying eggs internally to birth live young into the water, so they require no specialized mating area. However, they were never very common and are quite rare now. They can live 20-30 years. They dislike crossing old border lines. They are sometimes hunted for their fabulously beautiful hides. They will attack medium to large boats, but they rarely come onto the continental shelf. As long as they stay in the water and just nudge at a boat, they can usually be discouraged with distance weapons. Once a sea serpent wraps around a boat, however, the best attack is to sever the spine, which is challenging to accomplish before the coils crush the hull.

Before Upheaval: Two species existed, both uncommon. They ranged through eastern and western oceans.

Sundered Times: One population of the eastern sea serpent survived in shard #33. One population of the western sea serpent survived in time shard #58.

Modern Times: The eastern sea serpent is mottled black and white, similar to a snowflake eel; it has red eyes. So far, this species remains in shard #33 due to its reluctance to cross former time barriers, although something may push it farther eventually. It is rare. The western sea serpent is brilliantly colored in bands of navy, royal, and turquoise blue divided by narrow lines of lemon yellow; it has pumpkin orange eyes in a royal blue head. It has spread from time shard #58 to shards #59 and #11, driven across barriers by foul weather or fierce rivals/enemies. Storms could drive it further. Due to conflicts with humans, it is increasingly rare.